Sulfur electrode container and methods of manufacture

ABSTRACT

A sulfur electrode container is described which includes a metallic liner in foil form with at least two full windings within an outer casing. The liner is substantially corrosion resistant to liquid sulfur, while the outer casing is readily corroded by liquid sulfur. One method of making a sulfur electrode container includes forming a metallic liner in foil form into at least two full windings within the outer casing. Another method of making a sulfur electrode container includes wrapping a metallic liner in foil form into at least two full windings around a sulfur-carbon plug, after which the plug surrounded by the foil, is positioned within an outer casing.

This invention relates to a sulfur electrode container and to methods offorming such containers and, more particularly, to such a containerincluding a metallic liner in foil form with at least two full windingswithin an outer casing and to methods of forming such containers.

Sodium-sulfur cells, which operate at elevated temperatures, are knownin the prior art as, for example, described in U.S. Pat. No. 3,946,751issued Feb. 18, 1975, under the title "Cell Casing with a HermeticMechanical Seal and a Hermetically Sealed Sodium-Sulfur Cell".

In U.S. Pat. No. 3,959,013, there is described a cathode cell casingportion, a cell casing and a hermetically sealed sodium-sulfur cell. Acathode cell casing portion is formed from a metal selected fromaluminum, steel or iron-nickel-cobalt alloys. A corrosion resistant andelectronically conductive layer adheres to the inner surface of thecontainer, which layer is selected from the class consisting ofmolybdenum and graphite. One suitable method of applying and adheringthe molybdenum layer to the inner surface of the cell casing portion isto plasma spray such surfaces with a thin layer of molybdenum. Theabove-identified patents are assigned to the General Electric Company.

In U.S. Pat. No. 3,140,006, there is described a pressure vessel forcontaining hydrogen or mixtures thereof. In column one, lines 24-30,there is pointed out that vessels for containing hydrogen are knownwhich have a plurality of layers or sections wherein only the innerlayer or layers are resistant to hydrogen and the outer section orsections are of carbon steel.

The patent describes an improved construction for a pressure vesselhaving a suitable opening for admitting a fluid which comprises at leasttwo sections which are not metallurgically bonded, either directly orindirectly, and which have a gas-flow passage therebetween. The innersection is or contains a layer of material which is resistant todeterioration by gas, such as hydrogen absorbed in the metal. The outersection has weep holes inter-connecting the inner surface thereof withthe outside of the vessel. The outer section may then be constructed ofcarbon steel. This description is set forth in column two, lines 6-15and in column three, lines 56-59. In column three, lines 43-47, it ispointed out that the sheel contains an inner section consisting of twolayers which may be bonded together as by rolling the layers ofdifferent metals to form a unitary sheet. The bonding may also beaccomplished by welds.

As opposed to the above patents, the present application describes andclaims a structure in which an inner metallic liner is provided in foilform with at least two full windings within and in contiguous relationwith the inner surface of an outer casing. The present sulfur electrodecontainer does not have and would not function with weep holes in theouter casing as described in U.S. Pat. No. 3,140,006.

In U.S. Patent application Ser. No. 837,381, filed Sept. 28, 1977, underthe title "Sulfur Electrode Container Construction and Method ofManufacture", now U.S. Pat. No. 4,131,226 there is described a pluralityof sulfur electrode container constructions characterized by mild steeland discrete anti-corrosive liners disposed within the containers andmethod of manufacturing each. A discrete liner of a materialsubstantially non-corrodible by liquid sulfur is disposed within acontainer in substantially contiguous relation with respect to the innerwall of the container for sealing the same from the liquid sulfurtherein. A flexible anti-corrosion foil such as 347 stainless steel isrolled as a cladding into the shape of a cylindrical liner so that itfits snugly into the open ended rigid container. The edge margins of thefoil are disposed in slightly overlapping relation. The liner can bespot welded to the container along its overlapping edge margins. ThisU.S. application is assigned to the Electric Power Research Institute,Inc., subject to the reservation of license rights to the GeneralElectric Company.

Our present invention is directed to providing an improved sulfurelectrode container and improved methods of manufacturing suchcontainers over the above-identified patents and patent application inthat there is utilized a metallic liner in foil form with at least twofull windings within the outer casing of the container.

The primary objects of our invention are to provide an improved sulfurelectrode container and improved methods of manufacturing suchcontainers wherein a self-sealing effect is produced by the linerthereby minimizing creeping of the corrosive sulfur or vapor between theliner and the outer casing of the container.

In accordance with one aspect of our invention, a sulfur electrodecontainer includes a metallic liner in foil form with at least two fullwindings within an outer casing. The liner is substantially corrosionresistant to liquid sulfur, while the outer casing is readily corrodedby liquid sulfur.

These and various other objects, features and advantages of theinvention will be better understood from the following description takenin connection with the accompanying drawing in which:

FIG. 1 is a sectional view of a sodium-sulfur cell with a sulfurelectrode container made in accordance with our invention; and

FIG. 2 is a sectional view through the sulfur electrode container ofFIG. 1 taken on line 2--2 thereof.

In FIG. 1 of the drawing, there is shown a sodiumsulfur cell 10 of thetype described in above-mentioned U.S. Pat. No. 3,946,751 with theimproved sulfur electrode container of the present invention. Cell 10has a ceramic ring 11, an inner casing of a solid sodium ion-conductivematerial 12 with on open end 13, and a glass seal 14 sealing a portionof the outer wall 15 of the inner casing 12 adjacent its open end 13within and to the ceramic ring 11. An improved sulfur electrodecontainer 16 has an outer metallic casing 17 readily corroded by liquidsulfur, with opposite open ends 18 and 19 and a flange 20 at open end 18surrounding inner casing 12 and spaced therefrom.

A metallic liner 21 in foil form has two full windings 22 and 23 withincasing 17. Liner 21 of 347 stainless steel is substantially corrosionresistant to liquid sulfur. The outer surface of liner 21 is insubstantially contiguous relation to the inner surface of outer casing17. A metallic end cap 24 with a layer of liner foil 25 disposed on itsinner surface is fitted and sealed as by welding at 26 within andadjacent open end 19 of outer casing 17. A sodium container 27 hasopposite open ends 28 and 29 and a flange 30 at open end 28. Sodiumcontainer 27 extends in an opposite direction to sulfur container 16. Ametallic end cap 31 for opposite open end 29 of sodium container 27, hasa fill opening 32 in end cap 29, and a fill tube 33 affixed to end cap29 and in communication with fill opening 32.

Sulfur and sodium metallic containers 16 and 27 are shown joined toceramic ring 11 by a hermetic mechanical seal shown generally at 34thereby forming a continuous container. Seal 34 comprises a pair ofretainer rings 35, each of which is positioned between ceramic ring 11and an adjacent flange 20 or 30 of containers 16 and 27, respectively. Apair of "C" shaped sealing rings 36 are positioned similarly to rings 35but surround exteriorly and are spaced from rings 35. The open portionof each "C" shaped sealing ring faces outwardly. A retaining collar 37is positioned around each container and adjacent to the opposite surfaceof the casing flange. Each collar 37 has at least a pair of andpreferably a plurality of apertures 38 therethrough. The collars arepositioned so that the respective apertures 38 are aligned. Threadedfasteners 39, each passing through a pair of associated apertures, areemployed to tighten the mechanical seal to produce a hermetic mechanicalseal 34. Electrical insulation 40 in the form of fiberglass tape isshown wound around the exterior surface of containers 16 and 27 adjacentthe respective flanges 20 and 30 to prevent shortcircuiting of the cellby seal 34. Electrical insulation 41, in the form of an inorganic fibercloth ring is positioned between each flange 20 and 30 and the surfaceof each associated collar 37 to prevent short-circuiting of the cell byseal 34. While the opposite surfaces of ceramic ring 11 are smooth toinsure a good seal, there is shown also a preferred ring 42 of aluminumfoil between the opposite surface of retainer ring 35 and sealing ring36 and the associated surface of ceramic ring 11 to provide a smoothersurface. Hermetic mechanical seal 34 is shown in its tightened orhermetic position. A negative electrode 43 of sodium metal is positionedpreferably within inner casing 12 and partially within sodium container27. A positive electrode 44 of a sulfur-carbon plug is positionedpreferably within outer casing 17 and is in contact with outer wall 15of inner vessel 12 and with the interior liner 21. A void volume isprovided between ceramic ring 11 and the upper portion of positiveelectrode 44 to provide space for reactant during operation of the cell.Fill tube 33 is shown closed in any suitable manner such as by a weld45. End cap 31 is affixed to container 29 as by welding at 46. Theresulting structure is a hermetically sealed sodium-sulfur cell.

In FIG. 2 of the drawing, there is shown a sectional view through theimproved electrode container of FIG. 1 taken on line 2--2 thereof. Thesame numerals are used in the description of FIG. 2 as were employed inthe description of FIG. 1. Sulfur electrode container 16 has an outermetallic casing 17 surrounding inner casing 12 and spaced therefrom.Metallic liner 21 in foil form has two full windings 22 and 23 withincasing 17. The outer surface of liner 21 is in substantially contiguousrelation to the inner surface of outer casing 17. Negative electrode 43of sodium metal is positioned within inner casing 12. Positive electrode44 of a sulfur-carbon plug is positioned within outer casing 17 and incontact with outer wall 15 of inner vessel 12.

We found that we could form an improved sulfur electrode container whichincludes an outer metallic casing readily corroded by liquid sulfur,such as a low carbon steel. Another suitable outer metal casing materialis nickel. The outer casing has opposite open ends. It may be desirable,depending on the type of sulfur container and on the method of joiningsuch container to form a sodium-sulfur battery, to provide an outwardlyor inwardly extending flange to one open end of the casing. As it isshown in both FIGS. 1 and 2 of the drawing, an outwardly extendingflange is employed. Such a flange configuration is used in view of thehermetic mechanical seal employed in the sodium-sulfur battery in whichit is used. Since other sealing methods are available for affixing thesulfur electrode container as a portion of the sodium-sulfur cell, suchan outwardly extending flange might not be required. However, we willdescribe an embodiment of the electrode container of our invention whichcan be employed in the cell shown in the figures of the drawing anddescribed above. A metallic liner in foil form with at least two fullwindings, is provided within the outer casing. The liner issubstantially corrosion resistant to liquid sulfur. Suitable materialsfor the liner include various stainless steels such as 347 stainlesssteel and molybdenum, and nickel-chronium alloys such as a 50%nickel-50% chromium alloy.

We found that at least two full windings to form the metallic liner isrequired to eliminate or substantially reduce the creeping of thecorrosive sulfur or its vapor between the outer surface of the liner andthe inner surface of the container. Our present liner, by having atleast two full windings offers a self-sealing effect. It is preferredthat the liner be co-extensive with the length of the outer casing. Theouter surface of the liner is in substantially contiguous relation withrespect to the inner surface of the outer casing. A metallic end cap isadapted to fit and thereby sealed within and adjacent one open end ofthe casing. In the present embodiment, the metallic end cap will fitinto the open end opposite the open end having a flange thereat. Theinner surface of the end cap is substantially corrosion resistant toliquid sulfur. Thus, the end cap or at least that portion of the endcap, other than its inner surface, can be made of the same metal as theouter casing. The inner surface of the end cap can be formed of the samematerial as the liner or at least one layer of the liner foil can bedisposed on the inner surface of the end cap thereby making at least theinner surface of the end cap substantially corrosion resistant to liquidsulfur. If desired, at least one weld spot is employed to tack the linerto the inner wall of the casing. In the configuration of thesodium-sulfur cell shown in the figures of the drawing, a sulfur-carbonplug is fitted within the sulfur electrode container. The sulfur-carbonplug comprises generally a pre-cast cylindrical body of sulfur andcarbon mat with a central opening. The carbon mat is impregnated withsulfur. The sulfur-carbon plug is positioned within sulfur electrodecontainer so that its outer surface is in contact with the inner surfaceof the liner, its inner surface is in contact with the outer surface ofsolid sodium ion-conductive tube and its bottom end, as viewed in FIG.1, is in contact with the inner surface of the end cap. The end cap isfitted within the bottom opening of the sulfur electrode container asviewed in FIG. 1, so that the edges of the end cap are in contact withthe inner surface of the liner. The end cap is sealed to the outercasing and liner along its outer periphery, as for example by welding.

The sulfur electrode container is formed in one method by providing anouter metallic casing having opposite open ends and outwardly extendingflanges at one open end, which casing is readily corrodible by liquidsulfur. A metallic liner which is substantially corrosion resistant toliquid sulfur is provided in foil form. The foil is formed into at leasttwo full windings within the outer casing with the outer surface of theliner in substantially contiguous relation with respect to the innersurface of the outer casing. A metal end cap is provided which isadapted to fit and be sealed within and adjacent one open end of thecasing. The end cap is provided with at least its inner surfacesubstantially corrosion resistant to liquid sulfur. Although not shownin the embodiment being described, the liner can be welded whereby oneweld spot tacks the liner to the inner wall of the casing. This methodincludes further fitting the end cap within and adjacent the bottomopening of the sulfur electrode container as viewed in FIG. 1 of thedrawing, so that the edges of the end cap are in contact with the innersurface of the liner. The end cap is sealed to the outer casing andliner along its outer periphery, as for example by welding. This methodincludes further disposing at least one layer of the liner foil on theinner surface of the end cap so that the inner surface of the end cap issubstantially corrosion resistant to liquid sulfur.

The sulfur electrode container is formed in another method by firstproviding a sulfur-carbon plug. A metallic liner in foil form, which issubstantially corrosion resistant to liquid sulfur is then wrapped intoat least two full windings around the sulfur-carbon plug. An outermetallic casing having opposite open ends, readily corrodible by liquidsulfur, is provided. The sulfur-carbon plug surrounded by at least twofull windings of the foil is positioned within the outer casing with theouter surface of the liner in substantially contiguous relation withrespect to the inner surface of the outer casing. A metallic end cap isprovided which is adapted to fit and be sealed within and adjacent oneopen end of the casing. The end cap is provided with at least its innersurface substantially corrosion resistant to liquid sulfur. The methodincludes also fitting the end cap within the bottom opening of thesulfur electrode container as viewed in FIG. 1 of the drawing, so thatthe edges of the end cap are in contact with the inner surface of theliner. The method includes further sealing the end cap to the outercasing and liner along its outer periphery as, for example, by welding.The method includes disposing at least one layer of the liner foil onthe inner surface of the end cap whereby the inner surface of the endcap is substantially corrosion resistant to liquid sulfur.

As shown in FIGS. 1 and 2 of the drawing, a hermetic mechanical seal isemployed to seal the sulfur electrode container in the sodium-sulfurcell. It will be appreciated that there are other methods of sealing thesulfur electrode container in a sodium-sulfur cell, such as sealing theflange of the sulfur electrode container to the ceramic ring by means ofa glass seal or by thermocompression bonding. Thus, it will beappreciated that depending on the method of sealing the sulfur electrodecontainer in the sodium-sulfur cell, the metal end cap can initially orsubsequently be sealed to the liner and outer casing. Thus, for example,in the configuration shown in FIGS. 1 and 2 of the drawing, the outermetallic casing of the sulfur electrode container without the end capcan be hermetically sealed to the ceramic ring. The metallic liner canthen be inserted within the outer casing. The pre-formed sulfur-carbonplug can then be inserted within the liner to surround the sodiumionconductive electrolyte tube. Thereafter, the end cap can be fittedand sealed to the outer casing and liner. Using the same configurationas shown in FIGS. 1 and 2 of the drawing, the outer metal casing canhave its liner inserted therein. The end cap is then sealed to the outercasing and liner. The sulfur-carbon plug can then be inserted within theliner from the opposite open end of the sulfur electrode container. Thesulfur electrode container, including the sulfur-carbon plug, can thenbe hermetically sealed by means of its flange to the ceramic ring in thesodium-sulfur cell.

Examples of sulfur electrode containers and method of manufacturing suchcontainers made in accordance with our invention are set forth below:

EXAMPLE I

A sulfur electrode container was formed as above described and as isshown in FIGS. 1 and 2 of the drawing by providing an outer metalliccasing of low carbon steel having opposite open ends, which container isreadily corrodible by liquid sulfur. An outwardly extending flange isprovided at one open end of the outer casing. A 2 mil. thick 347stainless steel foil, which is substantially corrosion resistant toliquid sulfur, was formed into two full windings within the outer casingthereby providing a metallic liner. The outer surface of the liner wasin substantially contiguous relation with respect to the inner surfaceof the outer casing. A metallic end cap of low carbon steel having onelayer of liner foil disposed on its inner surface was fitted within andadjacent the open end of the casing opposite the open end with theflange so that the edge of the end cap was in contact with the innersurface of the liner. The end cap was sealed by welding the cap to theliner and outer casing. The resulting device was a sulfur electrodecontainer made in accordance with our invention.

EXAMPLE II

A sulfur electrode container is assembled by providing a sulfur-carbonplug with a central opening extending partially therethrough. A 2 mil.thick 347 stainless steel foil, which is substantially corrosionresistant to liquid sulfur is wrapped around the sulfur-carbon plug toprovide two full windings of the foil around the plug. An outer metalliccasing of 2 mil. thick 347 stainless steel foil is provided. The casing,which is readily corrodible by liquid sulfur, has opposite open ends anda flange at one open end. A metallic end cap of low carbon steel isfitted within and adjacent the open end opposite the open end with theflange. The end cap has one layer of liner foil disposed on its innersurface. The end cap is sealed to the outer casing by welding. Thesulfur-carbon plug surrounded by the two full windings of foil arepositioned within the outer casing with the outer surface of the linerin substantially contiguous relation with respect to the inner surfaceof the outer casing. This device is a sulfur electrode container made inaccordance with our invention.

EXAMPLE III

The sulfur electrode container of Example I was employed in asodium-sulfur cell of the type described above and shown in FIGS. 1 and2 of the drawing. The cell had a ceramic ring of alpha alumina, an innercasing of solid sodium and beta alumina in tube form with one open end,and a glass seal sealing a portion of the outer wall of the inner casingadjacent its open end within and to the ceramic ring. A sodium containerof metal had opposite open ends and a flange at one open end. An end capwas welded to the open end of the sodium container opposite to the openend having a flange. A fill opening was provided in the end cap and afill tube affixed to the end cap and in communication with the fillopening.

A ring of aluminum foil was positioned on the upper surface of theceramic ring. A retainer ring is positioned on the upper surface of thealuminum foil and surrounded by "C" shaped sealing ring with its openingfacing outwardly. The flange of the sodium container is positioned onthe upper surface of both the retainer ring and the "C" shaped sealingring. Fiberglass tape was wound around the exterior surface of thesodium container adjacent its flange. An inorganic fiber cloth ring waspositioned around the upper surface of the flange of the sodiumcontainer.

The sulfur electrode container of Example I had a sulfur-carbon pluginserted therein through its open end. The sulfur electrode container,with its plug positioned therein surrounded the beta-alumina tube,whereby the tube was fitted into the opening within the sulfur-carbonplug. As described above, the sulfur-carbon plug was positioned on theopposite surface of the ceramic ring in the same manner as was thesodium container. A retaining collar was positioned around eachcontainer and adjacent to the opposite surface of the casing flange.Each collar had a plurality of apertures therethrough. The collars werepositioned so that the respective apertures were aligned. A threadedfastener passed through each pair of associated apertures. Thesefasteners were then tightened to provide a hermetic mechanical seal forthe cell. The threaded fasteners were tightened to a pressure of about300 lbs. to provide a complete hermetic mechanical seal.

EXAMPLE IV

The cell of Example III was positioned in a furnace and heated to a celloperating temperature of 315° C. The cell was charged and dischargedover 80 cycles in a completely satisfactory manner. Subsequently, thecell was disassembled and the inner surface of the liner and of theouter casing of the sulfur electrode container were examined. Thecontainer showed only nominal amounts of corrosion products.

While other modifications of the invention and variations thereof whichmay be employed within the scope of the invention have not beendescribed, the invention is intended to include such as may be embracedwithin the following claims:

What we claim as new and desire to secure by Letters Patent of theUnited States is:
 1. A sulfur electrode container for use as a portionof a sodium-sulfur cell which comprises an outer metallic casing readilycorroded by liquid sulfur, the outer casing having opposite open ends, ametallic liner in foil form with at least two full windings within thecasing, the liner substantially corrosion resistant to liquid sulfur,the outer surface of the liner in substantially contiguous relation withrespect to the inner surface of the outer casing, a metallic end capadapted to fit and to be sealed within and adjacent one open end of thecasing, and at least the inner surface of the end cap substantiallycorrosion resistant to liquid sulfur.
 2. A sulfur electrode container asin claim 1, in which at least one weld spot tacks the liner to the innerwall of the casing.
 3. A sulfur electrode container as in claim 1, inwhich the end cap is fitted and sealed within and adjacent one open endof the casing.
 4. A sulfur electrode container as in claim 1, in whichat least one layer of the liner foil is disposed on the inner surface ofthe end cap.